doc: do not document commands that are already deprecated

doc: do not document commands that are already deprecated

The command 'ftdi_location' is deprecated and a TCL procedure is
in place to direct the user to the replacement command.
There is no need to document the deprecated command.

Remove 'ftdi_location' from the documentation.

Change-Id: Ia431c6b0e7444d3f3288c088429bfb47089ff1b5
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/6154
Tested-by: jenkins
Reviewed-by: Marc Schink <dev@zapb.de>